i've designed about 25 pages of a site and am handing over the psds so the in-house designers can build out the rest. i need to put together a toolkit and wondered if anyone had any examples they could share.

You can approach it similarly to doing it for print. Headlines styles are still a font, weight etc. with examples pictured. But you'd also add the accompanying CSS class and/or a heading tag (h1, h2) etc. Much of it can really be done the same as a print style guide. Start with what you know to get rolling then you can fill in the blanks later.